Radio receiving system



INVEN TOR Hls ATTORNEY Patented July 12, 1932 UNITED sTATEs HAROLD l'. ELLIOTT, vOl' PALO ALTO, CALIFORNIA, ASSIGNOR, BY EESN ASSIGNMENTS,

RADIO CORPORATION F AMERICA, 0F

NEW' YORK, N.. Y., A CORPORATION OF Application mea December 2a, 1925. semi No. 77,039.

m tuning adjustment is needed. This kind of y system is useful not only to enable a comparatively unskilled amateur operator to use his set in the most satisfactory manner, but also to' enable a skilled commercial operator to cover his range so that he may obtain the signals he is to receive to the substantial exclusion of all others2 and'- merely by the aid of simple manipulation..

It is another object of my invention to make 2 it ossible to accomplish these resultsby the 'bodiment of my invention; and

ai of inexpensive apparatus, requiringno intricate adjustments either in the rocess of manufacture or range the receiving system in such a way that it is necessary to tune only a single circuit by the aid 'of a variable element, which nee have but a comparatively small range of adlustment to take care of a very'broad range I, 1n the frequencies of the signals to be received. 4

I am enabled to secure these highly benecial results by combining the sifgnals received with locally generated radio requency energy, having a frequency that is substantially higher than the highest frequency to bereceived whereby the signals from then on are carried by these much higher frequency currents. Since it is possible so toparran e the system that this higher frequency is su stantially constant for all signals received, the subsequent detection and amplification can be arranged once and for all; and the single tuningfunction of ad'ustilng this frequency is al that' is require to set the system .into proper receptive condition. Of course for selectivityit is usually desirable to' provide a filter, andv one or two additional amplifiers operatingat successively lower frequencies.

B the aid of my invention, it is entirely feasible to detect and amplify lsignals carried m by electrical energy of frequency between 100 in operation. In act, I ar-` kilocycles (3000 meters) to 2,000 kilocycles (150 meters). Such a broad lie'ld rendersl it possible to allocate the frequencies among the various transmitting stations in a way .l that will ensure against appreciable interference, and to provide many more such stations. My invention possesses many otheradvantages, and has other objects which may be made more easily apparent from a consideration of several embodiments of my invention. For this purpose I have shown a form in the drawing accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understoodA that this detailed description is not to be taken in alimitingsense, since the scope of my invention is best defined by the appendedclaims.

Figure 1 is a Wiring diagramof one emlFigure 2 is a diagram of a modification.

For the purpose of presenting a concrete example lof my invention, I shall assume that the receiving systems illustrated are arranged to receive signals carried by radiations of between kilocycles and 2,000

Furthermore, in Fig. 1 I illustrate a scheme whereby the final translating device, such as a loud s eaker 11, and its connectionsare used also or forming an energy absorbing circuit, las disclosed and claimed in my Patent No.1,1,7 37 ,078 granted November 26, 1929, and entitled: Radio re- Y ceiving system. In thatv scheme, the leads v 12 connecting the. speaker 11 to the output terminals 13 of the last series of amplifiers 14, include coils 15 and 65, both of which serve as primaries of a transformer 16. This transformer serves to pass the received en- '9D er to further elements of the system, as

wil be hereinafter described; the metallic` arts of the loudspeaker llfcooperate with the earth, or' other separated metallic elements of the system, vto formv an .open absorbing circuit. In the present instance, one of the output terminals 13 is grounded 'at 17, in order to yprovide' a counterpoise for the loudspeaker. Since the theory of opera.- tion of suchj7 an-absorbing circuit is. adeirll Le? set, im is du in cientlv render the system seeciive,

scheme is rendered substantially clear of in` terference, even when signals are picked up differing by as little as kilocycles. Let it be assumed that a signal of 1000 Akilocycles is to be received, while at the same time, a

signal of 1015 kilocycles also affects the absorbing circuit. Both these signals will of course pass filter 19 or 55. The adjustable oscillator-detector unit 21 or 56 is adjusted to provide oscillations of 3,500 kilocycles, re-

acting with the 1000 kilocycle signal to give 2,500 kilocycles. The interfering' signal tiated in the 400 kilocycle detector and amplifier 34 or 59.- Of course it is possible to obtain 400 kilQcycle current in the output vof detector-oscillator` 33 or 58 by providing it with current of 1,700 kilocycles, but such a current cannot reach this unit due to the sharply tuned 2,500 kilocycle filter 32 or 57. The differentiation can be carried still further by the addition of a 350 kilocycle oscillator and detector 60, giving a kilocycle output :for the desired signal and 3,5 kilocycle for the interfering signal; these signals can very readily be differentiated. Anycurrent neighboring 300 kilocycles that would react to give 'a50 kilocycle output for the unit 60, is efficiently .prevented from doing so by the 400 kilocycle filter and amplifier 59. Y

This system of fiXe'd filter and .amplifier circuits, arranged in cascade, may be made to give any desired degree of selectivity. The

'first filter 30 or 57 is required to discriminate only between signalsv of 1,700 rand 2,500 kilocycles; the second filter 3ft-or 59, between signals of 300 and 400 kilocycles; and the third filter 61between 35 and 50 kilocycles,

in order that the discrimination as' a whole may be 15 kilocyoles. This vmakesit feasible todo awayvwith tuning the input circuit to the receiver, and to employ but a single adjustable circuit, the first oscillator, to produce a currentwhich when mingled with-the desired signal will give 2,500 kilocycles, or

whatever ot er.value it is desired-that the rst filter system should have.

` Generally it maybe stated that if the first filter is :tuned to 7n, cycles, and the succeeding filter to nl, then the first filter must eliminate -energy in the neighborhood of vif-211,1 cycles in order to prevent the intermediate oscillator from combining with interfering energy to produce an undesired signal of nl cycles.

VVResonant circuits can readily be designed to These have this desired degree of discrimination. Furthermore, as heretofore pointed out, only a small range of variation is required for the first oscillator to provide a broad range rej ception.

The condenser 27 of the first oscillator can obviously be made to vary the frequency or Wave length in any desired fashion. If a straight line frequency law is followed, and all broadcast stations between 100 and 2,000 kilocycles are separated by 15 lkilocycles, then all stations would be evenlyspaced over this range, and. over 125 separate stations may be accommodated in a given region.4

Since some o f the stations would have`limited sending radii, it is likely that several times this number can be o erated simultaneously within the United gtates, Canada,

and Mexico without material interference,.

and alike number i`n Europe. It would also be possible for a few very high power stations to use the relatively long Waves from 2,000 to 3,000 meters (100'to 150 kilocycles) without employing special receiving apparatusto detect their signals. Althoughl several European stations now operate in this range, they cannot be received in this' country Without unusual or special equipment.

l claim:

1. In a receiving system, a local oscillator of adjustable frequency arranged to heterodyne with the received signals to produce a constant frequency much higher than any to be received, a fixed filter for passing a narrow band neighboring said constant frequency, a fixed oscillator for reducing the said frequency by heterodyning to amuch lower constant value, and a filter passing a narrow bandneighboring said lower fre'- v quency. v

2. The method of receiving and selecting signals of wide frequenc range, which com- Apffses first increasing t e frequency of the signal toa definite, constant value, and then' ysuccessively ,operating upon the said higher frequency to reduce it to set, low values in order to impart selectivity to the system.

3. In a receiving system, adjustable means for'operating upon incoming signaling ime pulses to increase the frequency of the carrier current, to a definite, set value, and nonadjustablea means successively operating upon the said increased frequency to reduce itin stepsto set, -low values in order to im-f part selectivity tothe system.

4. The .method .of selectively receiving high frequency signals, which comprises shiftingthe carrier `frequency of the signalsl to a constant value higher than thehighest frequency to be received, and subsequently .reducing the carrier frequency to a lower value. l

5. The lmethod as set forth in claim 4, with the addition of the step of filtering the 'of receptiom'whereby the tunable apparatus need 'ne adjusted through a relatively small range to obtain the constant frequency for any signals within the said delinite frequency range.

7. The method of selectively receiving high frequency signals within a delinite fre- `quency range, which comprises picking upv the signa-l impulses, neat filtering the signal impulses so as to include only signals within said range, and raising the frequency of the desired signal to a definite constant value.

8. The method of selectively receiving high frequency signals Withinl a definite frequency range, which comprises picking up the signal impulses, next filtering the signal impulses so as to include only signals within said range, raising the frequency of the desired signal to a definite constant value,

iilterin the raised frequency signals to exclude a l except the constant frequency7 and azsl lastly lowering the frequency.

9. In a receiving system for high frequency signals, means for increasing the carrier frequency of the si nals to a constant value higher than ,the highest frequency to be received, and means for subsequently reducin the frequency to al lower fixed value.`

l0. n a receiving system for high frequency signals, means for increasing the carrier frequency of the 'signals toa constant value higher than the highestv frequency to be received, permanently adjusted means for filtering said higher frequency to exclude all but said higher frequency signal carrier, and means for subsequently reducing the frequency to a lower fixed value.

1l. The combination as set lforth in claim 10, inkwhich the means for reducing the frequency is permanently adjusted.

12. In a receiving system for high freuency signals that fall within a 'definite'.

requency range, means for picking up the signal impulses, means for excluding all signals outside the range, and means for raising the carrier frequency of the desired 'signal to a definite constant value.

13. In a receiving 'system for high. frequency signals that fall within a definite frequency range, 'means for picking up the signal impulses, means for excluding all signals outside the range, means for raising the carrier frequency ofthe desired signal to a definite constant value, permanently adjusted means for ltering said higher frequency 'v to exclude all lout said higher fl'equen Sigi nal carrier, and means for suhsequcnw y reducing the said higher frequency to a lower fixed value.

14.. In a heterodyne receiver, the combination with a radio frequency circuit for the reception ci" a certain range of signal irequencies, of means for producing local cscillation frequencies and a. heat frequency therefrom, which heat frequency added to.

said range or" oscillation frequencies provides a range of image frequencies relatively widely separated from and corresponding to said range ci signal frequencies.

l5. The method for the heterodyne reception of radio signals Vwhich comprises selecting a range oi frequencies to he received, applying a range ci' frequencies thereto to produce a constant heat frequency therefrom throughout said range, said heat frequency and said range of oscillation frequencies heing such that an image frequency range is produced thereby which is relatively widely separated from the range of signal' requency to he received. y

ln witness whereof l have hereunto set my hand.

, E. ELLIOTT. 

